1. Field of the Invention
The present invention relates to the field of antennas. Specifically, it relates to phase-controlled antennas including phased arrays.
2. Related Art
Array antennas refer to the class of antennas which provide radiation formed by phase-coherent combining of outputs from (or inputs to) multiple antenna elements. The antenna characteristics are determined by the spatial position of individual radiators and the amplitudes, phases, and time delays of their respective excitation(s). Advantages provided by array antennas include the ability to control the radiation and reception pattern of an antenna by changing the excitation across the array aperture. For example, the antenna main beam can be very rapidly scanned without having to mechanically reposition the antenna. It also provides the ability to modify the pattern to suppress interference or to otherwise enhance the spatial coverage which the antenna is to provide.
In many array applications, the relative phase response at each element is controlled via a device called a phase shifter. Different types of phase shifters rely on various physical mechanisms to effect a change in phase response. At microwave frequencies, phase shifters are typically implemented as switched lengths of transmission line (e.g., strip line) or resonant circuits, the former implementation having a larger bandwidth than the latter.
In the past, switching between different antenna element feed ports has been used to select elements of multi-element antennas, to control element gain, to adjust the antenna element impedance, and to change the polarization response of the antenna. To our knowledge, switched feeds on the same antenna element have never been used to achieve controlled phase shifts nor has varactor-based selection between plural modes of antenna resonance been used to implement controlled phase shifts. The most closely related prior art in our present view (U.S. Pat. No. 5,434,575) describes a relatively complex, multi-element antenna that switches among pairs of antenna elements for selectively changing the sense of circularly polarized antenna operation.
It is assumed that the reader will have a general background in RF circuits and antennae. However, if not, for general background information reference may be had to texts such as, for example:                Hansen, R. C., Phased Array Antennas, John Wiley & Sons, 1998        Kraus, J. D., and Marhefka, R. J., Antennas for All Applications, McGraw-Hill, 2002        Pozar, D. M., Microwave Engineering, Addison Wesley, 1993.        